Global flag to identify update.php run, and so avoid various unwanted
operations, such as hook_init() and hook_exit() invokes, css/js preprocessing
and translation, and solve some theming issues. This flag is checked on several
places in Drupal code…

The command was aborted because the user chose to cancel it at some prompt.
This exit code is arbitrarily the same as EX_TEMPFAIL in sysexits.h, although
note that shell error codes are distinct from C exit codes, so this alignment
not meaningful.